This study will correlate the results of clinical measures of contrast sensitivity, visual acuity, and visual fields with the ability of low vision patients to identify correctly symbols at intermediate distances. The study aims to develop these tests so that they correlate well with performance in visual tasks, and to detemrine the role of apparent size and contrast in the identificaiton of objects by patients under several conditions of visual impairment. The long term benefits will be derived through improved diagnosis of visual disabilities and improved low vision therapy. Approximately 100 subjects ranging from 20 to 80 years in age will be used in the study, and will have lost sight to one of three diseases: retinitis pigmentosa, diabetic retinopathy, or maculopathy. Forty normally sighted, age matched control subjects will also participate in the study. Each subject will have his acuity measured using the acuity chart employed in the Early Treatment Diabetic Retinopathy Study at a test distance of 2.4 meters, and a background luminance of 100 cd/m2. The results will be recorded as log minimal angle of resolution (MAR). Visual fields will be measured using a Humphrey Model 610 automated perimeter. Threshold static fields will be determined for the central 40 degrees of vision, and the results will be recorded as log threshold sensitivity versus weighted eccentricity, the weighting funciton having been derived from previous studies. These points will be reduced to a measure of the mean slope, which will be normalized to the results from the normally sighted subjects. Contrast sensitivity at five spatial frequencies will be determined through a two alternative forced choice procedure at a distance of 1.5 meters using the Nicolet Optronics CS 2000 system. The field tested will subtend 8.6 by 10.6 degrees visual angle, and the space averaged luminance will be 100 cd/m2. Symbol identification will be assessed using a four alternative forced choice procedure to detemrine the probability of correct identification of four non-verbal symbols at each of seven sizes and two contrast levels. The test distance will be 1.5 meters and the background luminance will be 100 cd/m2. The results of all tests will be checked for multiple correlations and collinearities, and models of symbol identification performance will be developed using the results of the clinical tests as predictor variables.